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Equipped with a distributed electric propulsion system, eVTOL is the primary vehicle for future urban air mobility. The electrical machine determines the weight of the distributed electric propulsion system, and the cooling capability determines the electrical machine’s weight. The electrical machine with air cooling is preferred for eVTOL due to its simplicity and light weight. This paper presents a new air-cooling system for an electrical machine in an electric ducted fan propulsion system. The novel cooling system consists of a cooling guide vane with a heat pipe (CGVHP), which is located downstream of the ducted fan rotating blade. The heated end of the heat pipe is inserted into the stator end windings and the cold end is inserted into the cooling guide vane. The heat generated in the windings is transmitted to the cooling guide vane by the heat pipe and dissipated by the forced convection using low-temperature air passing through the ducted fan. The cooling performance of the cooling guide vane with the heat pipe was numerically simulated, considering several critical design factors. The simulation results showed that the proposed CGVHP can be helpful for reducing the winding temperature of the electrical machine by over 25.5 °C at the peak power condition of 15.7 kW.

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Electric ducted fan has newly emerged as the most compact type of propulsion fan for flying cars, because of its flexible configuration arrangement, low noise level and high safety level operation. Typically, an electric ducted fan is composed of a hub-driven fan and a hub-mounted inner rotor electrical machine. The thermal management of the hub-mounted electrical machine is essential because it determines the machine’s continuous output power and reliability, as well as the fan thrust force. The heat transmitted from the stator winding to the cooling fin is dissipated by introducing the air flow at hub region to the cooling fin. Therefore, in order to better improve the thermal performance of the cooling fin, an aerodynamic design of cooling fin is proposed in this paper for better thermal management of stator end-windings. Firstly, for a certain desired power output of electrical machine under temperature constraints of stator winding, lumped thermal network is established to derive the requirement of heat transfer coefficients of the cooling fin. Then, from engineering feasibility, three different cooling fin designs including straight type, arc-shape type and airfoil shape type are tested by computational fluid dynamics. The evaluation of the cooling fin designs includes the flow characteristics, power requirements and thermal characteristics for stator winding cooling purposes. In comparison with the conventionally straight type cooling fin, improvements are gained from the designed arc-shape type and airfoil shape type cooling fin configurations, whereas the fan thrust force remains the same simultaneously. It is verified that the arc-shape type and airfoil shape type cooling fins are promising in enhancing the thermal management performance of the electrical machine stator winding with little power requirement.